Recently, carbon dioxide (CO2) discharged from industrial factories have been pointed out as a main culprit of global warming, accordingly, research to fix carbon dioxide and use microalgae as a bioenergy source has been actively conducted. The microalgae can function to treat waste water and fix carbon dioxide because of various abilities thereof, and have been used for the purpose of producing useful materials such as fuel materials, cosmetics, feed, food coloring, and medical raw materials, and a utilization range of the microalgae has expanded due to the continuous discovery of useful high-value materials.
Many factors such as composition of a culture medium, temperature, acidity (pH), intensity of light, and amount of light are present as a matter affecting an increase in weight of living bodies and useful products of the microalgae, but among the factors, the proportion of light is largest due to a property of photosynthetic microalgae.
Generally, apparatuses for cultivating the photosynthetic microalgae for the purpose of securing a biomass and fixing carbon dioxide may be largely divided into an apparatus of performing large-scale outdoor cultivation (open system) and an apparatus of using a photobioreactor (closed system). In the case of the apparatus of performing large-scale outdoor cultivation, which includes a pond type, reaction facilities such as a lake or large-scale pond type have been mainly used, and commercialized in some countries.
However, the aforementioned type of cultivation facilities have merits in that an initial investment cost is low and maintenance is easy, but installation thereof has no choice but to be extremely restrictive because of problems such as contamination, difficulty in separation and purification, a low cell concentration, a large substrate amount (particularly, nitrogen source), requirement of high water quality and large water amount, an irregular climate condition, and high personnel expenses. Particularly, there are demerits in that since light is not effectively transmitted into the cultivation apparatus, a growth rate of a fungus body is slow, growth yield of the fungus body is low, and a wide installation space is required in order to remove a large amount of carbon dioxide.
In order to solve the aforementioned problems of the apparatus of performing large-scale outdoor cultivation, efforts for producing products in an amount that is the same as or larger than the amount in the apparatus of performing large-scale outdoor cultivation and producing high-quality products including useful materials at a higher concentration by performing high concentration cultivation through a small-scale reactor are being made.
As a currently developed type, there are a general agitation-type reactor, a plate-type reactor, a pipe-type reactor, a column-type reactor, and the like, and in all kinds of the reactors, effective transmission of light is considered as a most important point in design of the reactor. When the concentration of the microalgae cell is low, a culture medium, injection of gas, and the like are the most important factors, but when the concentration reaches a high concentration, the intensity of light becomes the most important factor. This is because as the concentration is increased, a penetration length of light is shortened.
That is, in the case of light applied while the microalgae are cultivated, a population number is gradually increased while the microalgae grow, and thus the microalgae existing on the surface of the reactor can continuously receive light, but the microalgae in the reactor cannot receive a sufficient amount of light required in growth because a shadow effect is formed due to the microalgae of the surface.
In order to solve this problem, Korean Patent No. 10-0933741 discloses a photobioreactor for cultivating microalgae in a large amount. In the disclosed reactor, a LED and a flexible LED are used as a plate-type light source, and the reactor has a structure where the light source comes into direct contact with a cultivation solution.
However, in the photobioreactor having the aforementioned structure, there is a problem in that, since microalgae are attached to the surface of the light source, light efficiency is reduced.
Further, as a technology relating to the photobioreactor, Korean Patent Application Laid-Open No. 2002-0008825 discloses a photobioreactor of producing biological resources, which includes an apparatus causing turbulence fluidization, a device introducing light into a reactor chamber, and an apparatus injecting air at a lower side of the reactor chamber. However, the aforementioned photobioreactor adopts a structure where algae and air are mixed by injecting air at the lower side, but has a problem in that when an injection pressure of air is reduced, the algae may be added into the apparatus injecting air.